This invention relates to transducing heads used with disc drive storage systems. More particularly, this invention relates to the orientation of the read gap element and the write gap in dual gap magnetic heads used with rotary actuators.
Magnetic disc drive systems have become widely accepted in the computer industry as a cost effective and reliable form of data storage. The advantages of disc drive technology over other means of data storage include an increased data transfer rate and storage capacity.
In a magnetic disc drive storage system, a magnetic disc rotates at a high speed while a magnetic read/write head "flies" over the surface of the rotating disc. As the disc rotates, aerodynamic properties cause the magnetic head to glide on a cushion of air suspended over a surface of the disc. The storage disc carries information on concentric data tracks. Information can be retrieved from the disc surface by moving the magnetic read/write head between data tracks.
In general, there are two types of actuators which are used to position the magnetic head over the disc surface, linear and rotary. A linear actuator moves back and forth linearly in a direction measured from the center of the rotating disc. Rotary actuators require less space than linear actuators, working much like a tone arm on a record player as it positions the magnetic head along an arc over the surface of a magnetic disc. The arcuate path of the rotary actuator arm, however, can introduce a skew angle between the magnetic read/write head and the data track.
A dual gap magnetic head uses a read gap for reading information and a write gap for writing information. Dual gap magnetic heads allow magnetic head designers to optimize performance of the read gap and the write gap. For example, a magnetoresistive head uses a read gap for a magnetoresistive readback element and a write gap for inductively writing magnetically encoded information. Design constraints require that the two gaps be physically separated from each other.
Performance of a dual gap magnetic head can be optimized for a particular data track on a magnetic disc by aligning the write gap with the data track when writing information and aligning the read gap with the data track when reading information. Using a linear actuator, this alignment is not a problem. However, a rotary actuator introduces a skew angle between data tracks and the axis of a dual gap head. For example, a dual gap head having 320 micro inches of separation between the two gaps and a 9.degree. angle skew angle with a data track will have an offset of 50 micro inches.
An actuator controller which determines the position of the actuator can compensate for the skew angle introduced by a rotary actuator. Still, the skew angle significantly contributes to error due to track misregistration. Track misregistration occurs when the skew angle between the data track and the dual gap magnetic head causes the read gap to be positioned such that it is trying to read along a portion of the track where there is no information written. More particularly, when information is written onto a magnetic media disc, the write gap imprints information onto the disc in an area defined by the width of the write gap. A smaller read gap is placed behind the write gap to read information previously written onto the disc. Since the read gap is smaller than the write gap, extra data or disc space is available on both edges of the read gap. As a rotary actuator arm swings from one edge of the magnetic media disc to the other, the skew angle changes. The dynamic skew angle causes the position of the read gap to change relative to the write gap. In some rotary actuator positions, the read gap may actually swing out beyond the write gap. When this occurs, the read gap is attempting to read information in a location where there is no data written onto the magnetic media disc. Alternatively, the read gap may read undesired information from an adjacent data track.